1. Field of the Invention
The present invention relates to a method for fabricating a color filter substrate of a liquid crystal display (LCD) panel, and more particularly, to a method for fabricating a color filter substrate including a process key.
2. Description of the Related Art
An LCD panel mainly includes an upper substrate and a lower substrate, and utilizes a liquid crystal driven by an applied signal to display an image. In general, the upper substrate is regarded as a color filter substrate for displaying an image in color, and the lower substrate is regarded as a thin film transistor array substrate on which unit pixels are arranged in a matrix configuration. Each of the unit pixels is provided with a thin film transistor (hereinafter, referred to as TFT) as a switching device.
Next, the structure of an LCD panel including an upper substrate 150 and a lower substrate 100 will be described with reference to FIG. 1. As shown in FIG. 1, a plurality of gate lines 101 are arranged parallel to one another on the lower substrate 100, and a plurality of data lines 102 are arranged parallel to one another and perpendicular to the gate lines 101. Unit pixel regions are defined by intersection of the gate lines 101 and the data lines 102, and are arranged in a matrix configuration on the lower substrate 100. Also, a switching device TFT 103 for driving the unit pixel is formed at each intersection of the gate and data lines 101 and 102. The TFT 103 includes a gate electrode, source and drain electrodes and a channel layer. The gate electrodes are connected to the gate lines 101. The source and drain electrodes are connected to the data lines 102.
In addition, pixel electrodes 104 for supplying an electric field to a liquid crystal 110 are formed on the lower substrate 100. An alignment layer (not shown) for aligning the liquid crystal 110 is formed on the pixel electrodes 104 over the entire lower substrate 100. The alignment layer is formed of an organic material such as polyimide by a rubbing process such that the alignment layer is rubbed with a rubbing cloth or the like after having been applied. Moreover, spacers (not shown) for maintaining a uniform cell-gap between the lower substrate 100 and the upper substrate 150 are distributed at regular intervals. A sealant (not shown) is formed along an outer edge of a pixel region of the lower substrate 100 to prevent leakage of an injected liquid crystal 110 and to bond the upper substrate 150 and the lower substrate 100.
Next, a process for fabricating an LCD panel having such a structure will now be described with reference to FIG. 2. The LCD panel includes a TFT array substrate on which TFTs are arranged in a matrix configuration and a color filter substrate for displaying color information. The process for fabricating the LCD panel includes a step for forming the TFT array substrate, a step for forming the color filter substrate, which is a separate step from the step of forming the TFT array substrate, and a cell step for forming a unit LCD panel by attaching the TFT array substrate and the color filter substrate.
The step for forming the TFT array substrate includes forming a TFT, and forming an alignment layer for aligning a liquid crystal on a substrate. The forming of the TFT further includes forming gate electrodes and gate lines, a gate insulation film, a semiconductor layer, source and drain electrodes and data lines, and a pixel electrode on the substrate. The forming of the alignment layer further includes forming an organic layer such as a polyimide layer and a rubbing process for rubbing the alignment layer with a rubbing cloth or the like. After forming the TFT and before forming the alignment layer, a process may be added for forming spacers maintaining a cell-gap between the TFT array substrate and the color filter substrate.
The process for forming the color filter substrate includes a step for forming a color filter layer, a step for forming an alignment layer, and a step for forming a seal pattern. The step for forming the color filter layer includes forming a black matrix, an overcoat layer and a common electrode. Then, the step for forming the alignment layer is performed thereon. The step for forming the alignment layer includes applying an alignment layer such as polyimide and rubbing the alignment layer with a rubbing cloth or the like. After forming the common electrode and before forming the alignment layer, a process may be added for forming spacers. Here, since the spacers maintain a cell-gap between the TFT array substrate and the color filter substrate, the spacers may be formed on either of the TFT array substrate or the color filter substrate.
After the step of forming the alignment layer, a seal pattern is formed along an outer edge of a pixel region of the color filter substrate to maintain a liquid crystal injected as well as the cell-gap. Alternatively, the seal pattern may be formed on the TFT array substrate according to circumstances.
Next, the cell step is performed to fabricate a unit LCD panel by attaching the TFT array substrate and the color filter substrate which have been fabricated through separate processes. The cell step includes an attachment, a cut, and a liquid crystal injection. The attachment is performed such that the TFT array substrate and the color filter substrate face each other and are attached together. The attached upper and lower substrates are coupled by the sealant, and the cell-gap is maintained. Here, when the TFT array substrate and the color filter substrate are arranged to face each other, a high precision is required. In addition, a black matrix is formed on the color filter substrate to cut off unnecessary light irradiated from the TFT array substrate. However, the unnecessary light may be leaked even by a minute misalignment. Therefore, to prevent a misalignment of the upper substrate and the lower substrate, alignment keys are formed at the upper substrate and the lower substrate. By detecting the alignment keys during the attachment process, a precise alignment of the substrates is performed.
The alignment key is needed not only in a process for attaching the upper substrate and the lower substrate but also in other processes for forming the upper substrate or the lower substrate to precisely align the substrate on a stage to perform each process. Particularly, the alignment key used to arrange the substrate in each process is called a process key, and a plurality of process keys are formed on an outer edge of the pixel region.
Next, a process for fabricating a color filter substrate with the process key will be described with reference to FIGS. 3 and 4.
After the attachment of the lower and upper substrates, a cut process is performed to divide the attached substrates by the unit cell. Since a plurality of unit LCD panel regions are simultaneously formed on a large-sized mother substrate to improve productivity, the mother substrate is cut into a plurality of the unit LCD panels. After the cut process, the liquid crystal is injected into each unit LCD panel, and then a liquid crystal injection hole is sealed, thereby completing fabrication of the LCD panel. As mentioned above, to fabricate a high quality LCD panel, the color filter substrate and the TFT array substrate should be precisely aligned with a difference range of less than a few micrometers.
Next, a process for fabricating the color filter substrate having various process keys will now be described with reference to FIG. 3 and FIGS. 4A to 4C. FIG. 3 is a plan view showing that a color filter layer and a process key are formed on a substrate 301. A process key 310 for precisely aligning the substrate 301 in various processes is formed at an outer edge of a pixel region. By recognizing the process key 310 with a camera or the like mounted at each stage where a process is performed, it is determined whether the substrate 301 is arranged well or not.
FIGS. 4A to 4C are views taken along line I-I′ of FIG. 3 to show a sequential process for fabricating the color filter substrate including the process key according to the related art. As shown in FIG. 4A, a black matrix pattern 302 is formed on the substrate 301. The process key 310 embossed on an outer edge of a pixel region is made of a material for the black matrix 302, which may be formed of a metallic or resin material. The black matrix 302 made of resin is mainly used to fabricate a large-sized LCD device.
In a process for forming the black matrix 302 on the substrate 301, a photosensitive resin for the black matrix 302 is deposited on the substrate 301, and then an exposure using a mask having a certain pattern, a development and a cleaning are performed, thereby forming the black matrix pattern 302. Therefore, a mask process is needed for forming the black matrix pattern 302.
Next, as shown in FIG. 4B, after the black matrix pattern 302 is formed, red, blue and green (R, G and B) color filter layers 303a, 303b and 303c are formed on the substrate 301. The color filter layers 303a, 303b and 303c may be formed by a method such as a printing method, an electrodepositing method, a dyeing method, a pigment dispersing method or the like. In the pigment dispersing method, one of R, G and B photoresist color filter layers 303a, 303b and 303c is formed on the substrate 301 on which the black matrix 302 has been formed, and then an exposure process using a mask, a development and a cleaning process are performed thereon, thereby forming a color filter layer at a predetermined pixel region. To form the color filter layers of various colors, each of R, G, B color filter layers 303a, 303b and 303c passes through the mask process.
Next, in FIG. 4C, an overcoat layer 304 of an organic material for compensating a step difference between the color filter layers 303a, 303b and 303c is formed. The overcoat layer 304 is unnecessary when the step difference between the color filter layers 303a, 303b and 303c does not exist, but the overcoat layer 304 is commonly formed when the resin black matrix 302 is used. After the overcoat layer 304 has been formed, a common electrode 305 for supplying an electric field to a liquid crystal is formed. The common electrode 305 may be formed of an ITO (indium tin oxide), a transparent electrode. After the formation of the common electrode 305, spacers 306 for maintaining a cell-gap between the lower substrate and the upper substrate are formed. The spacer 306 may be formed by various methods such as a scattering method, a nonelectrostatic scattering method, and a patterning method or the like. After the formation of the spacer 306, a process for forming an alignment layer 307 for aligning the liquid crystal is performed. After that, a sealant may be formed along an outer edge of a pixel region to prevent leakage of the liquid crystal injected and maintain the cell-gap between the attached substrates. The color filter substrate is thus completed.
In the process for forming the color filter substrate, the substrate 301 is required to be precisely arranged. For example, the substrate 301 and the mask should be precisely arranged to perform a predetermined mask process. To this end, an image of a process key is detected by a camera or the like which is mounted at a predetermined position, and then it is determined whether the substrate 301 is arranged well or not by comparing the detected information with a predetermined data. More importantly, high precision with a difference range of less than a few micrometers (μm) is required when the upper substrate and the lower substrate are attached.
However, in the related art, a separate mask is applied when the process for forming the black matrix 302 is performed, which delays a process performance. Also, because the mask process is followed by an exposure, a development, and a cleaning process, a lot of equipment are needed to perform such processes, thereby causing a delay in the whole fabrication process and deterioration of the LCD panel.